It is frequently necessary in the care and treatment of some patients to monitor body temperature for extended periods of time and, in the case of neonatal and premature infants, to also control external environmental temperature, for example by infrared heating, in order to maintain a desired body temperature. The sensing element of the temperature probe is mounted directly on the patient's body with a probe cover that adhesively secures the sensing element to the body and also thermally insulates the sensing element from the external environmental temperature so that the temperature sensing element and the temperature monitor and/or temperature controller controlled thereby,can properly respond to the temperature of the patient's body.
Medical temperature monitoring and controlling devices are generally adapted to use replaceable temperature sensing probes provided the probes have a preselected temperature-resistance characteristic compatible with the monitor design. Medical temperature sensing probes in general comprises a thermistor temperature sensing element having electric contacts and lead conductors connected to contacts. Medical temperature monitoring devices made by different manufacturers and for different uses are frequently designed for use with temperature probes having different temperature-resistance curves. For example, four single-thermistor type medical temperature sensing probes in common use for neonatal care have measured resistances at 25 degrees Centigrade of about 2,050 ohms; 2,252 ohms; 6,867 ohms and 10,000 ohms and there is also a dual thermistor probe with three wires having a dual resistance of 6,000 and 30,000 ohms at 25 degrees Centigrade. The temperature-resistance characteristics of the thermistor are dependent on the resistivity of the thermistor element, the thickness of the element between the contacts, and the area of the contacts. The resistance of the thermistor is adjustable during manufacture of the thermistors by removing some of the surface area of the electric contacts to produce a probe having a preselected resistance at a selected temperature such as 25 degrees C.
Prior temperature sensing probes have used metal wire conductors to connect the temperature sensing elements to the temperature monitor and controller device. However, metal wires create distinct lines and shadows within X-rays that are taken of the patient and such picture obstructions cause concern and aggravation to the radiologist and increase the possibility of misinterpretation of the X-ray. Further, metal wires generally have high thermal conductivity and if portions of the metal wires proximate to the temperature sensing element are exposed to ambient conditions which either heat or cool the wire, the metal wire can conduct heat to or away from the temperature sensing element and produce an inaccurate body temperature reading. Prior efforts to overcome this problem included use of temperature probe covers large enough to also cover and hold a portion of the lead wires adjacent the sensing element against the patient's body to not only shield the wire from ambient conditions but also warm or cool the wire to the patient's body temperature.